In conventional earth borehole operations such as drilling, the casing, liner, or drill string (collectively “tubular string”) is made up of sections or joints of threaded tubular members, generally about 30-40 feet long, which are sequentially threaded together as the tubular string is advanced into an earth borehole. Accordingly, it is necessary for the drilling or casing running operations to be intermittently interrupted so that successive joints of tubular members can be attached, and the drilling or casing running operations continued. When threaded drill pipe or casing is employed and the next joint is ready to be attached, the drilling or casing running operations are stopped, and the tubular string in the earth borehole is suspended with slips or the like forming part of the wellhead assembly. The next joint is then stabbed into the suspended tubular string and made up, and the running operations then continued. Operations such as making and breaking threaded connections are time consuming and, more importantly, inherently dangerous to personnel on the rig floor. Furthermore, during the time when the next joint is being attached to the suspended string, fluid circulation operations involving drilling mud or casing running fluids are stopped. In conventional drilling or casing running operations using jointed tubular members, continuous circulation is thus not practical since, as noted above, during the period when a successive joint is being added, circulation operations are stopped. Continuous circulation is desirable to maintain the annulus between the casing string and the borehole clear and to prevent bridging. It is also desirable, during casing running operations, that the casing string suspended in the earth borehole be kept filled with fluid to prevent excessive fluid pressure differentials across the casing string, and thereby prevent collapse and/or blowouts.
Casing has been used as a drill string such that once the earth borehole has been drilled to the desired depth, the casing forming the drill string can be cemented in place in a conventional manner. This technique eliminates the need for separate drill strings and casing strings. Usually, when the casing string is used as the drill string, the end of the casing string in the earth borehole is attached to a disposable or retrievable bottomhole assembly which includes a motor and a drill bit. When the drilling operation is completed, the bottomhole assembly can be retrieved and the casing string in the borehole then cemented in place in a conventional manner. While drilling with casing clearly has advantages in terms of savings of time and money compared to conventional earth borehole drilling operations involving separate drill strings and casing strings, present methods for drilling with casing employ jointed casing with all the attendant problems discussed above with respect to jointed drill strings and/or casing strings.
Coiled tubing having a size of less than 3 inches or less has been uncoiled from the reel and inserted in threaded casing in a well. Although coiled tubing is not normally used in conjunction with cementing operations, it has been known to uncoil tubing from a reel into a well with a damaged casing, and then to cement the annulus between the tubing and the damaged casing in order to continue recovery from the well.
Those familiar with coiled tubing operations recognize that coiled tubing sizes conventionally extend up to about 3 inches, and that casing sizes typically extend to about 4 inches to about 7 inches or more. Coiled casing according to the present invention will thus typically have a diameter of 4 inches or more, and will commonly have a diameter of 4½ inches or 5½ inches.
U.S. Pat. No. 3,724,567 discloses a system for handling drill pipe or tubing for workover operations. The threaded tubular string may be a continuous piece moved from a storage position to the well U.S. Pat. No. 4,100,968 discloses a technique for running casing using a powered rotating tool. U.S. Pat. No. 5,197,553 discloses a retrievable bit and downhole motor at the lower end of a tubular drill stem, and U.S. Pat. No. 5,271,472 discloses a bit assembly including radially extendable and retractable arms with cutters that may be withdrawn through the drill stem.
U.S. Pat. No. 5,215,151 discloses a drilling technique with a continuous length of jointed coiled tubing. Hydraulic fluid may be pumped through the tubing string, and a wireline used to retrieve the bit. U.S. Pat. No. 5,547,314 discloses a system for storing and running jointed tubulars into a well. U.S. Pat. No. 6,250,395 discloses a system for installing and retrieving threaded pipe in a well. U.S. Pat. No. 5,641,021 discloses a well casing drill tool with closing sleeve.
U.S. Pat. No. 6,419,033 discloses a system for drilling a well with a bit and an underreamer. U.S. Pat. No. 6,439,866 discloses a downhole motor with a sealed bearing. U.S. Pat. No. 6,443,245 discloses a casing shoe. U.S. Pat. No. 6,513,223 and 6,585,052 disclose tubing centralizers. U.S. Pat. No. 6,564,868 disclose a tool and method for cutting a tubular. U.S. Pat. No. 6,705,413 discloses a technique for drilling with casing using a retrievable bit.
The prior art has not disclosed techniques for significantly reducing the cost of running casing in a well, and accordingly significant costs and risks are incurred both in running a casing in a well and in retrieving the casing string from a well.
The disadvantages of the prior art are overcome by the present invention, and improved equipment and techniques for running casing in a well is hereinafter disclosed.